IDS Forum

RE: backup strategy using HDS - shadow image, true copy

Posted By: Martin Fuerderer
Date: Tuesday, 30 November 2004, at 4:50 a.m.

In Response To: RE: backup strategy using HDS - shadow image, true copy (Lavoie, Diane)

Hi,

things to watch when using external backup and restore:

- always backup all chunks of the system within one
bracket of "onmode -c block/unblock" commands.
Partial backups are not supported (for restore).
- Therefore during backup, all dbspaces and chunks
must be online (i.e. may not be down).
- Also backup mirror chunks.
- If a (yet undetected) corruption exists during backup,
it will be restored as well and then cause a problem
when applying logs. Possibly use "oncheck" to detect
a problem before backup, or do a test-restore (on a
different system) to verify that a backup is good.
- Always restore the complete backup, including the
mirror chunks. Partial (cold) external restores followed
by warm external restore are not recommended/supported
with external backup and restore.

Note:
- There's no easy way to verify correctness/completeness
of a backup as the backup is done by external means
and ON-Bar cannot check it.
- It is possible to optimize with mirror chunks by backing
up only one "copy" of a mirrored pair of chunks.
But you are responsible for:
- restoring the backup to both, primary and mirror chunk,
- during backup to pick the correct chunk (and not a chunk
that may be down). I.e. if primary chunk is down you need
to backup the mirror chunk instead and vice versa.
- Such "mirror-optimized" backup can be tricky and error prone.
Make sure you have well-tested scripts that reliably select
chunks for backup and correctly restore them.

Following these recommendations should avoid corruptions
or similar problems with external backup and restore.

Apart from this, a problem can be a down BLOBSpace chunk
when a log file is backed up (where this log file contains log
records that reference a BLOB in the down BLOBSpace). Older
versions of IDS may not report the problem prominently.
But during log restore and recovery (after external physical
restore) there will be a problem with applying these log records,
possibly resulting in inconsistencies. However, this is a general
problem, not just with external backup and restore.

Regards,
Martin
--
Martin Fuerderer
IBM Informix Development Munich, Germany
Data Management Solutions

forum.subscriber@iiug.org wrote on 29.11.2004 18:23:57:

> Hi,
>
> We are using 7.31FD2,FC6 and 9.31.
>
> The corruption was either when changing the status to Online, we lost
one
> mirror of the logdbs or
> when applying the logs, one chunkd was offline.
>
> Diane
>
> -----Original Message-----
> From: Martin Fuerderer [mailto:MARTINFU@de.ibm.com]
> Sent: Monday, November 29, 2004 4:39 AM
> To: Lavoie, Diane
> Cc: forum.subscriber@iiug.org; ids@iiug.org
> Subject: RE: backup strategy using HDS - shadow image, true copy [3791]
>
>
> Hi,
>
> the description of what you're doing sounds about right.
> (BTW: we call it "External Backup and Restore".)
>
> What version of IDS are you using ?
> Can you describe the corruptions and the circumstances
> where they occurred in more detail ?
>
> Regards,
> Martin
> --
> Martin Fuerderer
> IBM Informix Development Munich, Germany
> Data Management Solutions
>
> forum.subscriber@iiug.org wrote on 26.11.2004 20:06:29:
>
> > we are using the onmode -c block/unblock commands to synchronize the
db
> and
> > using the onbar -r -e (external backup tools) to recover it.
> >
> > we did many recovery test, with log and without logs, most of the time
> > successfully except for these 4 times that I got the corruption.
> >
> > External backup tools are not supported by Informix, but onmode and
> onbar
> > cmds exist for this type of backup......
> >
> >
> >
> > -----Original Message-----
> > From: Robert Roussey
> >
>
[mailto:IMCEAEX-_O=SPIRITAIR_OU=RESCT_CN=RECIPIENTS_CN=ROBERTRO@SpiritAir.co
> > m]
> > Sent: Friday, November 26, 2004 1:55 PM
> > To: Lavoie, Diane; ids@iiug.org
> > Subject: RE: backup strategy using HDS - shadow image, true copy
[3789]
> >
> >
> >
> > Neither of those will work because they totally ignore the Informix
> > timestamp (used for all backups and restores) that exists on every
data
> page
> > and in the system catalog. The only way those utilities would work is

> if
> > you shut down informix and did them.
> >
> >
> > Bob Roussey
> > Spirit Airlines
> > Informix/Unix Administration
> > Phone: 586.741.8991
> > e-mail: RobertRo@SpiritAir.com
> >
> > -----Original Message-----
> > From: forum.subscriber@iiug.org [ mailto:forum.subscriber@iiug.org
> > <mailto:forum.subscriber@iiug.org> ] On Behalf Of Lavoie, Diane
> > Sent: Friday, November 26, 2004 11:28 AM
> > To: ids@iiug.org
> > Subject: backup strategy using HDS - shadow image, true copy [3789]
> >
> > Hi,
> >
> > We are presently testing shadow imange and true copy, as a backup
> solution
> > for our Informix database.
> >
> > This will replace the Informix Onbar backups. While performing some
> recovery
> >
> > testing using this new
> > method, I got corrupted database.
> >
> > Anybody using shadow image or true copy as database backup solution?
Any
>
> > comments will be much appreciated.
> >
> > Regards
> >
> >
> >
> >
>

Messages In This Thread

• backup strategy using HDS - shadow image, true copy
  Lavoie, Diane -- Friday, 26 November 2004, at 11:27 a.m.
  • RE: backup strategy using HDS - shadow image, true copy
    Lavoie, Diane -- Friday, 26 November 2004, at 2:06 p.m.
    • RE: backup strategy using HDS - shadow image, true copy
      Martin Fuerderer -- Monday, 29 November 2004, at 4:43 a.m.
    • RE: backup strategy using HDS - shadow image, true copy
      Lavoie, Diane -- Monday, 29 November 2004, at 12:23 p.m.
      • RE: backup strategy using HDS - shadow image, true copy
        Martin Fuerderer -- Tuesday, 30 November 2004, at 4:50 a.m.
  • AW: backup strategy using HDS - shadow image, true copy
    Andreas.KUTSCHE@spar.at -- Monday, 29 November 2004, at 3:39 a.m.

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